In the 21st century, due to the improvement of technology and the richness and development of the implantation theory, dental implantation has become a mature clinic technology for partial anodontia repairing. It does not only achieve the recovery of the function of missing teeth, but also restores the aesthetic appearance of natural teeth. As one of the basic elements for a successful implanting, the osseointegration between the dental implants and the surrounding osseous tissue has been the focus and investigation hotspot for a long time. Only when a dental implant reaches an osseointegration with the surrounding alveolar bone can it function to support and fix the prosthesis and perform its normal functions. Different designs of dental implants and different surface modifications on dental implants affect the progress and rate of the osseointegration of the implants, and the ultimate objects of seeking better bone healing speed and osseointegration rate are to shorten the treatment period, increase the bonding strength between the dental implants and the osseous tissue, and improve its stability and supporting capacity. Therefore, the biomechanic assessment on the dental implant/bone interface has became one of the important topics in the study of osseointegration, and, at present, a main research target is to find an study means that can harmlessly and precisely reflect the mechanical behavior, i.e., stability, of the bone-implant interface in the dental implant healing progress, and make a continuous observation possible, that is, an assessing method that is suitable for the clinical research on dental implant osseointegration in order to assess the level of the osseointegration of dental implants in an objective fashion. Resonance frequency analysis, as a mature technique for studying structure object and structural mechanics characteristics, has a potential to provide an effective approach for achieving the above target. That idea was seriously proposed by Meredith and Huang in the 1990s, after which, however, many basic and clinical studies proved that the dental implant resonance frequency analysis method they established cannot precisely and objectively reflect the bone healing progress of the dental implants and the interface bonding characteristic, which results in that the result of a single measurement does not possess practical clinical guiding significance. The underlying cause of the above problem is that Meredith and Huang simply chose the bending vibration mode as the study object when studying the resonance frequency of the dental implants. Although the bending vibration mode has advantages such as the easiness of being triggered and being identified and caught by instruments, it cannot directly reflect the mechanical behavior of the dental implant-bone interface, while torsional vibration is the very mode ideal for revealing the structural characteristic of the dental implant-bone interface.
Taking an overview on the study approach of dental implant osseointegration, besides histologic methods, biomechanic study is one of the important approaches, and is especially more important in clinical research. Many research techniques have emerged on dental implant osseointegration strength and dental implant stability.
Dental implant push-out test and spin-out test are commonly used mechanic study approaches for dental implant osseointegration at present, and as they provide the maximum disruptive strength of the dental implant-bone interface, they are destructive test methods, cannot be used to continuously observe the dental implants over time, and, furthermore, they are not suitable for clinical research. Dental implant percussion is a qualitative examining method for clinically deciding the stability of the dental implants and the presence of osseointegration, but it lacks an objective quantitative criteria. The Periotest mobility meter, invented according to the damping principle, overcomes the shortcomings of subjectivity and qualitativeness of simple percussion of dental implants, by outputting the mobility of dental implants as Periotest values (PTVs), which are generally between −5 and +5. However, the method has a poor repeatability, wherein the operation manner greatly affects the results, and investigation proves that the measured numerical values cannot precisely reflect the biomechanic nature of the bone-implant interface of dental implants.
Objects having masses and structures made up by such objects have their intrinsic frequencies, which are decided by the stiffness of the objects as well as the interfacial stiffness between structures, and when an external energizing frequency overlaps with the intrinsic frequency of an object or a structure interface, resonance occurs. Resonance frequency analysis is already a mature technique for investigating object and structure interface stiffness. It was successfully applied to the investigation on the stiffness of human long bone in the 1990s, and its feasibility for serving as a method for assessing fracture union and osteoporosis has been preliminarily proven. The direct bonding between the dental implant and the osseous tissue is the foundation of its successful working. In the initial stage after the implanting, assimilation happens between the dental implant and the surrounding osseous tissue due to surgery trauma; and in the process of the bone healing, the stiffness of the interface bone and the osseointegration stiffness increase gradually. Experiments indicate that the binding stiffness of the dental implant-bone interface reflects the extent of bone healing. On the basis of the above principle, Meredith et. al. incorporated the resonance frequency analysis technique into the dental implant stability research, and made the first Osstell dental implant resonance frequency analyzer. Its principle of operation (see the schematic representations) is as follows: to secure a L-shaped amplitude transformer to the dental implant with screws, install two miniature piezoceramics transducers on the inside and outside of the amplitude transformer (wherein one of them is used to emit 5-15 KHz continuous sine waves to energize the amplitude transformer-dental implant vibration, and the other one is a receiving transducer for receiving the amplitude and the frequency of the amplitude transformer), record a curve diagram about the frequency and the amplitude by using an analyzer, and obtain the resonance frequency by calculating. What it measures is the resonance frequency of the dental implant at lower order bending vibration mode.
In the system comprising the dental implant, the surrounding jaw and the transducer, the resonance frequency of the dental implant is decided by multiple factors, which generally include the stiffness and mass of the dental implant, the vibration moment arm, the density and structure of the surrounding bone of the dental implant, the shear stiffness of the dental implant-bone interface and so on, and the vibration mode presents multiple modes including bending vibration, vertical vibration, horizontal vibration and torsional vibration. Therefore, the resonance frequency of the dental implant consists of a plurality of frequencies, rather than a single one, and presents multiple stages. Under different vibration modes, the factors that affect the resonance frequency vary, and the mechanical behaviors of the dental implant-jawbone structural system are reflected with emphasis in different aspects. Currently the research on the resonance frequency of dental implant is on the basis of the bending vibration mode of dental implant, and under the mode the resonance frequency is majorly decided by factors such as the structure and mass of the surrounding osseous tissue of the dental implant and the height the dental implant protrudes above the bone surface, and mainly reflects the stability of the dental implant. Due to being influenced by too many factors, the current dental implant resonance frequency analysis method based on the bending vibration mode cannot objectively and precisely reflect the mechanical behavior of the dental implant-bone interface and the osseointegration level, which results in that the result of a single measurement does not possess practical clinical guiding significance; additionally, the connecting location and the arrangement orientation of the transducer largely affects the measurement result, resulting in the doubt on its clinical and scientific application values.
It can be seen that, the afore-said prior art measuring methods of the stability of dental implants still present many defects, and thus urgently need improvement. Given the defects in the prior art stability measuring methods of dental implants, the inventor, based on rich practice experience and expertise, made the present invention by positive innovating, unceasing researching and designing, and repeatedly sample trial making and improving.